<!DOCTYPE html>
<html>
    <head>
        <style>
            html, body {
                margin: 0;
            }

            div {
                position: absolute;
                top: 25vh;
                left: 25vw;
                width: 50vw;
                height: 50vh;
                background-color: green;
            }
        </style>
    </head>
    <body>
        <div></div>
    </body>
</html>
